1. Technical Field
The present disclosure relates to a field emission cathode structure and a method for making the same.
2. Discussion of Related Art
Carbon nanotubes (CNTs) are electrically conductive along their length, chemically stable, and can have a very small diameter (much less than 100 nanometers) and large aspect ratios (length/diameter). Due to these and other properties, it has been suggested that CNTs can play an important role in many fields, such as in a field emission device.
At present, different methods are widely used for fabricating composite carbon nanotube structure. CNTs can be produced by means of arc discharge between graphite rods. Another method for fabricating a composite carbon nanotube structure has been disclosed in U.S. Patent Application No. 20060192475. However, this method is complex because the first CNTs should be separated from the first substrate by ultrasonic method, immersed into a solution, and then coated on the second substrate. Furthermore, while immersing the first CNTs into the solution, some catalysts on the surface of the first carbon nanotubes will drop off, such that only a few second CNTs can be obtained on the surface of the first carbon nanotubes. The first carbon nanotubes and the second carbon nanotubes form a structure, which can be used as a field emission cathode structure.
However, while this kind of field emission cathode structure is used to emit electrons, a shielding effect exists between two adjacent carbon nanotubes, because the carbon nanotubes of the second CNTs have the same length. Therefore, the electrons emission efficiency of the field cathode structure is relative low.
What is needed, therefore, is to provide a field cathode structure having relative high electron emission efficiency.